1. Field of the Invention
The present invention relates to an organic electroluminescent (OEL) display device, and more particularly to a thin-film-transistor (TFT) OEL device.
2. Description of Related Art
The display devices are very important interface for the communication between men and machines. In recent years, the flat panel display devices are widely used because of many advantages such as light-weight, low power consumption, mini-size and high compactness. For example, liquid crystal display devices with TFT switches made by amorphous silicon are very popular now. However owing to high requirements of the consumers, the liquid crystal display devices with TFT switches made by amorphous silicon cannot meet the requirement for rapid response time, high contrast, and high brightness. On the other hand, the OEL display devices with TFT switches made of LTPS (low temperature polysilicon) are display devices having the advantages to meet the market demand. However, there are lots of technical obstacles to be overcome.
So far, the present method for manufacturing the TFT OEL panels for display devices is achieved by forming LTPS TFT switches on a substrate first. Then cathodes or anodes of the OEL display devices are formed on the substrate after the LTPS TFT switches are available on the substrates. Subsequently, the organic electroluminescent medium (e,g, a hole injection layer, a hole transport layer, a light-emission layer, an electron transport layer, or an electron injection layer) and the other electrode (e.g. anode) is deposited on the substrate. However, the method illustrated above is time-consuming and lots of masks are needed.
Hence, it cannot be considered as an optimal method or design of integrating the LTPS TFT and the OLED techniques.
It is therefore an object of the present invention to provide a TFT-OEL device which combines the formation of the cathode material and the bus line of the LTPS panel into one processing step so as to increase the interface uniformity and the interface matching between the cathode material and the bus line and reduce the remaining stress.
Another object of the present invention to provide a TFT-OEL device which uses a low-resistance material such as aluminum or silver to reduce RC delay.
Another object of the present invention to provide a TFT-OEL device with a design of top-emitting structure (i.e. a cathode is close to the substrate) to significantly reduce the adverse effects such as interference, scattering and reflection caused by the transmission path of the emitting light in the layers and increase the luminescent efficiency and aperture ratio.
Another object of the present invention to provide a TFT-OEL device which combines the formation of the cathode material and the bus line of the LTPS panel into one processing step so as to increase the interface uniformity and the interface matching between the cathode material and the bus line, reduce the remaining stress, and even reduce at least one mask step of coating a cathode film on the OLED panel as involved in the conventional LTPS TFT panel process.
To attain the above-mentioned objects, a TFT-OEL panel according to the present invention comprises: a substrate; a plurality of stripes of first conductive lines mounted on the surface of said substrate; a plurality of stripes of second conductive lines mounted on the surface of said substrate, intersecting said first conductive lines; a plurality of functional elements located at the intersections of said first conductive lines and said second conductive lines, including a transistor having a drain, a source and a gate; a cathode mounted on the surface of said substrate and connected to said drain; an anode mounted over said cathode; and at least one organic electroluminescent medium sandwiched between said cathode and said anode; wherein said cathode and said first conductive lines are made of the same material; said first conductive lines and said second conductive lines are not directly electrically contacted at the intersections thereof; said source is connected to said first conductive lines; said gate is connected to said second conductive lines; said drain corresponding to said source is electrically connected to said source when an electric current flows through said gate; and said source, said gate and said drain are not directly electrically contacted at the intersection thereof.
To illustrate the present invention, exemplary embodiments of a TFT-OEL device will now be described with reference to the accompanying drawings.